Photo-electric means for reproducing sound from graphical records



Sept. 8, 1925. 1,552,926

R. HART PHOTO-ELECTRIC MEANS FOR REPRODUCING- SOUND FROM GRAPHICALRECORDS.

Filed Nov. 1. 1924 i l l i l l l h i lfi Yrs" Inventor,- l'ZuSseZZ.Zi'art .fmm

.Attorriey.

Patented Sept. 8, 1925.

RUSSELL HART, OF LOS ANGELES, CALIFORNIA.

PHOTO-ELECTRIC MEANS FOR REPRODUCING SOUND FROM GRAPHICAL REtJOBDS.

Application filed November 1, 1924. Serial No. 747,313.

To all whom it may concern I v Be it known that I, RUSSELL HART, acitizen of the United States, residing at Los Angeles, in the county ofLos Angeles and State of California, have invented a new and usefulPhoto-Electric Means for Reproducing Sound from Graphical Records, ofwhich a specification is set forth below. I 1

In this specification, and the accompanying drawing, Ishall describe andshow a preferred form of my invention, and specifically mention certainof its more important objects. I do not limit myself to the formsdisclosed, since various changes and adaptations may be made thereinwithout departing from the essence of my invention as hereinafterclaimed; and objects and advantages, other than those specificallymentioned, are included within its scope.

My invention relates to photo-electric means for reproducing sound fromgraphical sound records' In a general way its object is to improve thequality or fineness of sound reproduction so that, if the record trulyrepresents the original soundin quality, the reproduction will be truein quality also.

More specifically my principal objects are; first, to provide soundreproducing means adapted to respond to exceedin ly small variations ingraphical sound recor 8; second, to furnish facilities for obtaining thefull effect of the recorded overtones in the reproduction so that thequality of the reproduced sound will correspond very closely to theoriginal; third, to obviate the effect of stray noises in thereproduction due to mechanical vibrations; and, fourth, to secure theabove results by means of a paratus of great simplicity and relative ylo'w'cost,

My invention is particularly adapted for the reproduction of sound fromphotographic film records, but may be used also for reproducing fromother graphical sound records. I prefer to use a photographic filmrecord of substantially constant density and variable width, but a filmhaving a record thereon of uniform width and varying density may beused,with practically equal facility.

The objects of the invention are attained in the manner illustrated inthe accompanying drawing, in which- Figure'l is a diagram showing atypical arrangement of my apparatus for reproduclng sound from aphotographic film rec- Figure 2 is a front elevation of a portion ofaphotographic film with a sound record thereon; and a .gate throughwhich it is made to slide, and by which it is definitely positioned;

' Figure 3 is'a longitudinal section of the above gate and film; and aside elevation of a preferred type of photo-electric cell attached tothegate at the rear;

Figure 4 is a rear sectional elevation of the above cell;

Figure 5 is aside elevation of a preferred type of incandescent lamp Iusev as a primary light source in my apparatus; and

Figure 6 is a diagram, greatly enlarged and exaggerated,to illustratethe manner in which reflection of the light from the primary source maybe utilized for obtainmg a much attenuated image thereof for. use as asecondary source which is directly employed for the reproduction ofsound.

Similar reference numerals refer to similar partsthroughout the severalviews.

In apparatus of this general character,

,wherein a luminous rectilinear filament is employed as a source oflight, it has hitherto been the effort to makeuse of a very tenuousfilament in order to have the re ro- 4 duction as free as possible fromthe e ects of blurring inevitably accompanying the use of a wide band oflight. I have found that the light emanating from tenuous incandescentfilaments is very "far from constant as the result of unavoidablevibration,

and that this causes a distortion of the re? produced sound quite asobjectionable as the blurring. It is believed that the changes in lightemanation in such filaments, when subjected to vibration, is due tochanges in the electrical conductivity resulting from variations intension caused by the vibration; and I have found that relatively stoutfilaments do not give this trouble.

In my apparatus, therefore, I employ for the primary light source anincandescent.

lamp 7 having a relatively thick and strong rectilinearfilament 8, notappreciably-affected in light emanation by mechanical vibrations. Imount this lamp adjustably on a stand 9, which also adj ustablv supportsa small cylindrical mirror 10 serving as a secondary light source forthe reproduction of sound. a

It is well known that an object reflected from a cylindrical mirrorappears to be greatly attenuated in the direction of the axis of themirror, and that this effect hecomes more marked as the radius of thecylindrical surface is decreased. This effect is diagrammaticallyillustrated in Figintrinsic brilliancy thus becomes available. for soundreproduction by photo-electric.

means.

As illustrated, the soundrecord 13 consists of a photo-exposed anddeveloped area of substantially uniform. density and very much varyingwidth, appearing as a relatively narrow longitudinal band parallel to,

* and near one edge of, a motion picture film 14. It is usuallyp'referable'to have the outer edge 15 of this record rectilinear, and

- this edge may then be considered to represent the axis of abscissae ofa very irregular curve 13 corresponding to the recorded sound wave. Theordinates of the curve represent volume of sound, or loudness, and thedistance between peaks, or correspond.- ing points on the curve,correspond to p1tch. The overtones and fundamentals of the recordedsound determine the shape of curve 13. I

In prior applications for United States patents (No. 608,499 filed Dec.22, 1922 and No. 630,870 filed April 9, 1923) I have shown and describedmeans for producing such sound records as above described upon uniformlymoving photographic films. The recording process therefore need not bedescribed herein.

For reproducing purposes the type of photographic film record described,or a similarly produced type having a record of uniform width andvarying density, is made to travel at the recording speed through a gate16. This may be accomplished by driving the film sprocket 17 by means ofa motor 18, the film being unwound from reel 19 and re-wound upon reel20. Figure 1, being diagrammatic rather than pictorial, does notillustrate the mechanism by which reel 20 is driven to accomplish there-winding. Such means, however, are well known to those familiar withthe motion picture and allied arts.

The approved form of sound gate illustratedv comprises a fixed plate 21,having a hinged cover 22, and two pairs of polished raised runners 23and 24 between which the Runners 23 are fixed or made integral withplate'21, and runners 24 are pressed inwardly from cover 22 by springs26 guided by studs 27.

- Cover plate 22 is provided with a small rectangular aperture 28, andthere is a similar aperture 29 in the rear plate of the gate. Behind thelatter aperture'is mounted a suitable, highly sensitive, photo-electriccell 30. 1

The type of photo-cell here shown comprises a very fine platinum grid 31filled with selenium or other photo-active material, on a glass orquartz cover plate 32, and connected by platinized strips-33 to terminalwires 34. A cup 35 containing anhydrous calcium chloride is .sealed uponthe cover plate enclosing the photo-active ma' terial and grid.

A process for making an exceedingly sensitive and rapid photo-electriccell of the above described type has been fully described in UnitedStates Patent No. 1,491,- 040, issued to me on April 22, 1924:.

In operation my reproducing apparatus is assembled in the mannerindicated in Figure 1 with a lens system 36 intermediate cylindricalmirror 10 and gate 16. By means 'ofthese lenses a sharp secondary imageof the mirrored image of the luminous filament is focused upon the soundrecord of the film. This brightly illuminates an exceedingly narrowtransverse band of the record, and the light rays that pass through thefilm are variably modulated thereby and impinge upon the photo-electricgrid 31. This constantly varying light flux will proportionately varythe electrical resistance of the photo-active material in the grid, andthus make it possible to reproduce the original sound by telephonicmeans.

There are various well known means for amplifying a small electriccurrent, modulated by the action of a photo-electric 'cell, to make itavailable for operating loudspeaking devices. One method of domg this isillustrated diagrammatically in Figure 1, wherein certain standardelectrical devices are conventionally shown. In this diagram aloud-speaking instrument is indicated at 37, an audion at 38, a variableratio transformer at 39, a variable resistance at lO, and a condenser'at11. The diagram shows a satisfactory manner {for connecting thesedevices to batteries 42 and 43, with the photo-electric-cell 30 incircuit in the system. i

The use of quartz for plate 32, upon which the photo-active materialofthe cell is deposited, is desirable on' account of the optical.

may be. eliminated in the above described manner. Also that, b reason ofthe exceedingly thin band 0 light falling upon the'film, there ispractically no blurring of the reproduced sound due to overlapping p theefiects of adjacent portions of the sound record.

Having thus fully described. my invention, I claim: c

11. Photo-electric sound reproducing means comprising; a movable opticalfilm with a sound record thereon adapted for variably intercepting lightrays; a linear light source; and a cylindrical mirror whereby anattenuated image of said source may be thrown upon said record.

2. Photo-electric sound reproducing means comprising; a movable opticalfilm with a sound record thereon adapted for variably intercepting lightrays; a linear light source; a cylindrical mirror whereby an attenuatedimage of said source may be thrown upon said record; and aphoto-electric cell behind the record adapted for modulating. anelectric current by the rays transmitted by said record. w

v 3. Photo-electric sound reproducing means comprising; a movableoptical film. with a sound record thereon adapted for variablyintercepting light rays; a linear light source; a cylindrical m rroradaptedfor reflecting an, attenuated image of said source;

and a lens intermediate said mirror and said record whereby reflectedlight rays from the former may be focused upon the latter.

4. Photo-electric sound reproducing means comprising; a movable opticalfilm with a sound record thereon adapted for variably intercepting lightrays; a linear light source; a cylindrical mirror. adapted for refleeting an attenuated image of saidsource;

a lens intermediate said mirror and said I record whereby reflectedlight rays from the former may befocused upon the latter; and aphoto-electric cell behind the record adapt ed for modulatin an electriccurrent by the rays transmitted y said record.

5. Photo-electric sound reproducing rneans comprising the elements setforth in claim 4 in combination with; means for passing an' electriccurrent through said cell for modulat-ion thereby; and means forutilizing said modulated current for the reproduction/of sound. e 6.Photo-electric sound reproducing means comprising the elements set forthin claim 4 in combination with; means for passing anelectric currentthrough said cell for modulationthereby; and means for amplifying andtelephomcally utilizing said modulated current for the reproduction ofsound.

; RUSSELL HART.

